Pogostemon dielsianus Dunn in Notes Bot. Gard. Edinburgh 8: 159. 1913.

Hu, Guo-Xiong, Su, Ting, An, Ming-Tai & Wang, Xiao-Yu, 2021, Rediscovery of Pogostemon dielsianus (Lamiaceae, Lamioideae), a rare endemic species from southwestern China, after one century, PhytoKeys 171, pp. 61-73 : 61

Pogostemon dielsianus Dunn in Notes Bot. Gard. Edinburgh 8: 159. 1913. Figs 3 , 4

Lectotype

(designated by Bhatti and Ingrouille in Bull. Nat. Hist. Mus. Lond. (Bot.) 27: 99. 1997). China. Yunnan: Fugong, Valley of the Salween, between Shih-chi-ti and Shia-ku-ti, Salween-Irrawaddy Divide, 26°20'N, 1524-1829 m, November 1905, G. Forrest 875 (E [barcode E00087126, image!]; isolectotype: K [barcode K000249619, image!]).

Revised description.

Perennial shrubs, up to 3 m tall. Stems solid, gray, ground diameter to 3.5 cm, branches terete or angular, slightly dilated at nodes, the initial branches green, densely strigose-pubescent, 2-3-year-old branches yellow-brown, subglabrous. Leaves opposite; petiole 0.5-2.5 cm long; blade linear-lanceolate to lanceolate, 8-14 × 2-4 cm, papery, both sides densely strigose-puberulent when young, the mature gradually subglabrous, base cuneate, margin serrate, apex acuminate, lateral veins 3-6 pairs. Spikes 3.5-7 cm long, 8-12 mm wide, terminal and axillary, subcontinuous, basally somewhat lax, with more than two lateral branches, densely appressed pubescent except for corolla, pedunculate, 0.5-2 cm long; cymes sessile, 8-14-flowered, flowers sessile. Bracts 4-6.5 mm, bracteoles 1.8-2.3 mm. Calyx tubular, 3.5-4.5 mm long, 5-veined; teeth 5, triangular, 1/5-1/4 as long as the calyx tube. Corolla rose, 2-liped, 7-9 mm long, glabrous outside; tube cylindric, dilated at throat, ca. 2 × as long as calyx; upper lip 3-lobed, lobes triangular, subequal, 1.1-1.3 × 0.9-1.1 mm; lower lip entire, ca. 0.9 × 0.7 mm. Stamens 4, exserted from corolla; filaments 5.5-7 mm long, exserted portion ca. 3.5 mm. Style 6.3-8.5 mm long; stigma bifid, lobes subequal, 1.1-1.3 mm. Disc ca. 0.7 mm long. Nutlets 4, ca. 1.5 × 0.8 mm, lanceolate.

Distribution and habitat.

The type locality of Pogostemon dielsianus was recorded in Fugong County, northwestern Yunnan of China, which is the only historical known site until our new discovery. As coordinate information of the collection is incomplete due to the lack of longitude data, the precise situation of type specimen is unclear. Based on the latitude provided in the original record, the type specimen is more likely to be collected in the north of Lushui County, a neighboring county of Fugong (Fig. 5 ). Although the recently collected population was also discovered in north Lushui County, distribution of the two populations does not overlap because they are located on different sides of Nujiang River (Fig. 5 ). In accordance with type specimen record, P. dielsianus grows amongst thickets on dry rocky hillsides with elevations ranging from 1524-1829 m. The finding that the newly recorded population grows on the riverside indicates that P. dielsianus is more likely to occur in humid areas of dry hillsides. Actually, a similar habitat can also be found elsewhere in Nujiang Canyon. Potential populations of this species, therefore, may be discovered through further field investigation in this region.

Phenology.

Flowering and fruiting from November to December.

Conservation status and preliminary IUCN assessment.

Pogostemon dielsianus is historically known from only two specimens collected from the type locality (Fugong, Yunnan, China) in 1905, and it has not been recollected for the past 114 years until our expedition to Nujiang Canyon in 2019. In the newly recorded locality (Lushui, Yunnan, China), only about 10 mature individuals have been discovered. Due to the lack of exact geographical information of the type locality, it is difficult to confirm the number of individuals there. Based on current investigations and historical records, we inferred that mature individuals of this species may be fewer than 250, and no subpopulation contains more than 50 mature individuals. Therefore, under the IUCN criteria C2a(i) ( IUCN 2012), we propose that P. dielsianus should be classified as "Critically Endangered (CR)".

Additional specimens examined.

China. Yunnan: Lushui County, Daxingdi Town, Tuanjie Village, Luchuluo, amongst a thicket near the Luchuluo River, elevation 1786 m, 26°7.14'N, 98°53.78'E, 24 November 2019, Hu et al. 636 (GACP!, IBSC!, KUN!).

Notes.

Pogostemon dielsianus is morphologically similar to P. elsholtzioides and P. griffithii in having lanceolate leaves. However, P. dielsianus can be easily distinguished from P. elsholtzioides and P. griffithii by its longer and tubular calyx, smaller ratio of the length of calyx teeth and calyx tube and longer corolla, filament and style (Table 2 ). In addition, the geographical distribution of these three species is also different in that P. dielsianus is endemic to NW Yunnan, China, P. elsholtzioides is widely distributed in the Himalayan regions (Bhutan, India, and SE Xizang, China), and P. griffithii is endemic to Myanmar ( Bhatti and Ingrouille 1997; Yao et al. 2015; Yao and Ge 2018).

In the protologue, Dunn (1913) did not designate a type for the name Pogostemon dielsianus Dunn. Bhatti and Ingrouille (1997) indicated the specimen deposited in E and K as holotype and isotype, respectively. In fact, they effectively chose the lectotype for the name and the term “holotype” and “isotype” can be corrected as “lectotype” and “isolectotype” according to Article 9.10 of the International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) ( Turland et al. 2018).

Figures

Figure 3. Pogostemon dielsianus A floral branches B bract and bracteole C flower D dissected calyx E dissected corolla showing stamens F stamen G pistil. Drawn by Xiao-Yu Wang based on Hu et al. 636 (GACP).

Figure 4. Habitat and morphology of Pogostemon dielsianus A habitat B habit C leaf, adaxial view D leaf, abaxial view E inflorescence F floral branches G flower H Stamens and style. Photographed by G. X. Hu.

Figure 5. Current distribution of Pogostemon dielsianus.